1. Field of the Invention
The present invention generally relates to stable colloidal suspensions useful as lubricating oil additives for lubricating oil compositions.
2. Description of the Related Art
Compositions containing molybdic acid have been used as lubricating oil additives to control oxidation and wear of engine components. Since their discovery, such complexes have been widely used as engine lubricating oil additives in automotive and diesel crankcase oils and as an additive in some two-cycle oils to prevent valve sticking. Generally, these compounds are added to a dispersant inhibitor (DI) package that is then added to the engine lubricating oils.
In general, such compositions can be, for example, complexes of molybdic acid and oil soluble basic nitrogen containing compounds made with an organic solvent during a molybdenum-containing composition complexation step. The complexation step can be followed by a sulfurization step as disclosed in U.S. Pat. Nos. 4,263,152 and 4,272,387, the contents of which are incorporated herein by reference.
A problem associated with these compounds is that they are dark in color, particularly after sulfurization; the sulfurized compositions are extremely dark in color. For instance, the sulfurized compositions are measured at about 5 triple dilute (DDD) using an ASTM D1500 or ASTM D6045 colorimetric test. Since reduced color lubricating oils are highly desired in the marketplace, these dark compositions can only be used in limited amounts because of the impact they have on the finished oil color.
It would therefore be desirable to provide a lubricating oil additive which not only exhibits good frictional properties, oxidation inhibition and anti-wear performance for lubricating oil compositions but also allows for lower color of the lubricating oils.